This research is concerned with elucidating the mechanisms governing the secretion of hormones by pituitary glands and pituitary tumors. Hypothalamic catecholamines directly inhibit the secretion of prolactin but not growth hormone by the pituitary gland. We propose to study the specific biochemical and endocrinological functions of these catecholamines as they govern the secretion of prolactin. Specifically, we will study the binding characteristics of dopamine on the pituitary gland and determine whether similar sites exist on pituitary tumors. We will also determine the requirement for calcium in the dopamine binding studies because this ion is necessary for the catecholamine to inhibit the secretion of prolactin. Competitive binding studies will also be conducted with various pharmacological dopaminergic blocking agents to determine the characteristics of the catecholamine binding sites. Adenylate cyclase activation by prostaglandins may be an important mechanism for the control of growth hormone secretion. Adenylate cyclase is apparently not involved in the secretion of prolactin. Since these neuroleptic drugs inhibit the secretion of growth hormone but decrease the secretion of prolactin, we want to determine whether these drugs modify the adenylate and guanylate cyclase activity in the pituitary and thus influence hormone secretion. Other studies will be designed to determine if the administration of these drugs to rats modifies the hypothalmic releasing or inhibiting factor activities in the hypothalamus. Likewise the turnover of hypothalamic catecholamines will be investigated in rats bearing hormone-secreting pituitary tumors and following the administration of neuroleptic drugs. The effect of prolactin on ACTH secretion will be determined.